Heat treatment of magnesium alloys containing zirconium



' loys can be considerably increased if such alloys into the alloy takes place.

Patented Aug. 20, 1940 UNITED STATES PATENT OFFICE HEAT TREATMENT OF MAGNESIUM ALLOYS CONTAINING ZIRCONIUM Franz Sauerwald, Breslau, Germany, assignor, by

mesne assignments, to Magnesium Development Corporation, a corporation of Delaware No Drawing. Application May 12, 1939, Serial No. 273,292. In Germany June 4, 1938 form of a solid solution, to form zirconium hydride which is apparently much less soluble in the magnesium matrix and endeavours to separate out in an extremely finely divided form thereby effecting a hardening of the alloy.

Thefollowing table shows how the strength properties of various binary magnesium-zirconium alloys are changed by the heat treatment in an atmosphere of hydrogen.

6 Claims.

Tensile Yield point, strength, kgs. kgs. per g gg Alloy Anneal- Anneal per sq. mm.- sq. mm. D Percent mg mg I of Zr perature, time,

0. hours Before After Before After Before After treattreattreattreattreat treatment ment ment ment nient ment It has been further ascertained that in alloys which, in addition to up to 2% of zirconium, contain zinc and cadmium (singly or jointly) up to the limit of saturation for the formation of solid solutions between these last two metals, heat treatment improves the mechanical strength properties of such alloys even in the absence of hydrogen, the yield point, in particular, being very considerably raised in some cases. The

substantially exceed the amounts which can be taken up in solid solution,

Exhaustive metallographic researches have revealed that in the high magnesium range of the binary magnesium-zirconium system only a limited amount of zirconium can be taken up in solid solution in magnesium.

At temperatures of about 600 C. magnesium will absorb about 1% of zirconium into solid solution but the solubility of the zirconium decreases considerably as the temperature falls and is only very slight at room temperature. It has also been found that the mechanical-strength properties of the binary magnesium-zirconium alloys are not improved to any appreciable extent by heat treatment.

It has now however been ascertained that the mechanical strength properties of the alloys, especially the binary magnesium-zirconium alto meet the requirements imposed on cast alloys.

The heat treatment for such ternary or multiple alloys consists in annealing the cast and normally solidified (or also quenched) alloys at temperatures below the boundary line of separation of the zirconium, i. e. at temperatures between about 150 and 400 0', As a rule, a preliminary homogenising heat treatment at temperatures above said boundary line is not only unnecessary, but, if protracted, mostly results in the formation of an extremely coarse crystalline structure. The consequent deterioration of the mechanical properties is so considerable that it cannot be counteracted by the favourable effect of the aforedescribed annealing heat treatment.

The following examples show the influence of the aforedescribed annealing heat treatment on be annealed in the presence of hydrogen at temperatures at which a diffusion of the hydrogen The temperatures necessary for this purpose are in the region of about 300-600 C. and the improved properties of the alloys are apparently due to the fact that the hydrogen difiusing into the alloy combines with the zirconium present in the magnesium in the elongation slightly decreases but is still suificient the mechanical properties of various alloys containing zirconium.

about 400 C. until the desired improvement has taken place.

Tensile Yield point h Elongation Annealing strengt kgs. per its: Alloy T m Dura- Before After Before After Before After 5 tion, treattreattreattreattreattreathours ment ment merit ment ment merit 0.77 Zr A Zn 250 15 19. 8 22.0 6.8 11.0 15. 3 10. 2 0.7% Zr. 2.0% Zn. 250 15 21. 5 24. 9 9. 4 14. 2 12.8 9.2 2.0% Cd 0.7% Zr 3.0% Zn 320 24 23. 7 26. 5 11.9 16. 5 12. 8 8. 6 2.0% Cd 0.7% Zn 4.0% Zn. 170 63 26. 0 27. 1 15. 4 19. 2 8. 6 4. 8 2.0% Cd v I claim: 4. A process of improving the strength char- 1. A process of improving the strength characteristics of magnesium base alloys containing zirconium in amounts not greater than about 2 per cent, which comprises heating such alloys to temperatures between about C. and about .600 C. until the desired improvement has taken place.

2. A process of improving the strength characteristics of magnesium base alloys containing zirconium in amounts not greater than about 2 per cent, which comprises heating such alloys in the presence of hydrogen to temperatures between about 150" C. and about 600 C. until the desired improvement has taken place.

3. A process of improving the strength characteristics of magnesium base alloys containing zirconium in amounts not greater than about 2 per cent and at least one element of the group consisting of zinc or cadmium in amounts not substantially greater than the solid solubility of the respective elements of said group in magnesium, which comprises heating such alloys to a temperature within the range from about 150 to acteristics of magnesium base alloys containing zirconium in amounts not greater than about 2 per cent and at least one element of the group consisting of zinc or cadmium in amounts not substantially greater than the solid solubility of the respective elements of said group in magnesiumQwhich comprises heating such alloys to a temperature within the range from about 150 to about 400 C. for at least about 15 hours.

5. A process of improving the strength characteristics of binary magnesium zirconium alloys containing not more than about 2 per cent zirconium, which comprises heating such alloys in the presence of hydrogen to a temperature within the range from about 300 to about 600 C. until the desired improvement has taken place.

6. A process of improving the strength characteristics of binary magnesium zirconium alloys containing not more than about 2 per cent zirconium, which comprises heating such alloys in the presence of hydrogen to a temperature of the order of 450 C. for at least about 8 hours.

FRANZ SAUERWALD. 

